1. Field of the Invention
The present invention relates to a ferrite composition. More particularly, it relates to a low-fire ferrite composition and a process for manufacturing ceramic articles using such a composition.
2. Description of the Related Arts
Ni--Cu--Zn ferrites have been used for the manufacture of multilayer ceramic inductor devices. So as to improve the quality factor of the devices, Ni--Cu--Zn ferrites are usually co-fired with high electrical conductivity metallurgies such as silver, copper, or gold during the manufacturing process. In the case of copper, the manufacturing process is rather troublesome because the co-firing must be conducted in a reducing atmosphere to prevent the copper from oxidizing. Moreover, the polymeric binder added in the casting step becomes difficult to remove in the non-oxygen atmosphere and some organic residues will be left in the sintered bodies. On the other hand, for reasons of economy, it is preferable to employ silver rather than gold in the co-firing, which can be conducted in air and for which no external atmosphere control is required.
While carrying out the co-firing of Ni--Cu--Zn ferrite and silver, it is important to control the sintering temperature, which should not exceed 900.degree. C., and the densification should be completed as soon as possible to avoid silver diffusing into the ferrite bodies. Conventional ferrite compositions, however, have unsatisfactory density when fired at such low temperatures, and must be sintered at a temperature of about 1,100.degree. C. before a sufficient density can be achieved. Accordingly, it is desirable to develop a low-fire ferrite composition which can be sintered at a temperature below 900.degree. C. to a sufficient density in a short time.
U.S. Pat. No. 5,387,365 discloses a ferrite magnet of the formula MO.nFe.sub.2 O.sub.3, where M is Sr or Ba and n=5.0 to 6.2, calcined at 1275-1300.degree. C. for 15-60 minutes.
U.S. Pat. No. 5,530,416 discloses a ferrite core coated with borosilicate zinc glass. The ferrite core is produced by: adding a low-temperature-sintered oxidized metal, such as BiO.sub.2 and PbO, and a resin binder to a ferrite powder of Mn, Fe, Co, Ni or the like; mixing the material together; and sintering the molded article at a low temperature.
U.S. Pat. No. 4,956,114 discloses a sintered ferrite body which is fired at a relatively low temperature of up to 950.degree. C., the body comprising 10-83 wt % of Ni--Cu--Zn ferrite, 15-75 wt % of borosilicate glass, and optionally 2-15 wt % of boron oxide.
Japanese Patent No. 51-151,331 and U.S. Pat. No. 4,540,500 disclose a sintered ferrite composition which is fired at a temperature below 1000.degree. C., comprising 5 wt % of lithium borosilicate glass.